1. Field of the Invention
The present invention relates to a real image type of variable power view finder that is used, for example, in a compact camera. More precisely, the invention relates to an objective lens optical system of the viewfinder located on the side of the system that is close to an object to be photographed, an eyepiece optical system located on the side of the system close to a photographer's eye, and an aspheric lens system in which deterioration of image quality will not occur if an assembly error occurs, such as an eccentric arrangement of the lens, for example.
2. Description of Related Art
A conventional real image type of variable power view finder is usually comprised of an objective lens system, a prism optical system for inverting an image, and an eyepiece lens system. The objective lens system usually includes two lens groups; a negative lens group located close to an object to be photographed, and a positive lens group located close to a photographer's eye. The negative lens group is made of a single negative lens, and the eyepiece lens system is made of a single positive lens.
In a known image forming optical system, such as an objective lens system in a view finder or a picture taking optical system of a camera, an aspheric lens (lenses) has been used in the optical system to realize a simple and small camera, obtain a high image forming efficiency by using fewer lenses, and increase the magnification in case of a variable power optical system.
In a known real image type of variable power view finder, however, a half angle of view of the objective lens system on a short focal length side is 25.degree..about.27.degree.. No larger half angle of view can be obtained.
In a known real image type of view finder in which the eyepiece lens system is made of a single positive lens, as mentioned above, it is necessary to set a long focal length of the eyepiece lens system in order to provide space for accommodating an image erecting optical system. Consequently, angular magnification of a view finder tends, to become small, particularly in the case of a wide angle optical system.
It is theoretically possible to increase the angular magnification by shortening the focal length of the eyepiece lens system. This, however, reduces the distance between an object image formed by the objective lens system and the erecting optical system, making it impossible to provide a mechanism for moving a field frame, for example, upon taking a picture using a panoramic photographing function, in the space between the object image and the erecting optical system.
The use of an aspheric lens makes it possible to enhance the freedom of design, but remarkably deteriorates image forming efficiency in the event of an assembly error (mounting error), such as an eccentric arrangement (mounting) of the aspheric lens, or a manufacturing error thereof.
Two eccentric errors that occur in a lens are; lens surface eccentric error, in which a paraxial center of curvature of only one of the lens surfaces is deviated from a design optical axis of the associated optical system, as shown in FIG. 54a, and a lens eccentric error, in which paraxial centers of curvature of both the lens surfaces are deviated from a design optical axis of the associated optical system, as shown in FIG. 54b.